A technology described in Patent Document 1 is already known as an example of the control device described above. The technology described in Patent Document 1 discloses transition control that causes transition from a parallel mode using at least an internal combustion engine as a driving force source to an electric power mode using only a rotary electric machine as a driving force source. In the technology in Patent Document 1, the control device is configured to, after the transition from the parallel mode to the electric power mode is determined in a state in which a first engagement device is in a direct engaged state, when a rotational speed of the internal combustion engine decreases down to a predetermined rotational speed or less, start disengagement control for the first engagement device and start zero-torque control that causes output torque of the internal combustion engine to be zero, and after the first engagement device is disengaged, suspend combustion of the internal combustion engine.
The technology in Patent Document 1 is based on the assumption that a vehicle speed decreases after the transition from the parallel mode to the electric power mode is determined, that is, a case is supposed in which the transition from the parallel mode to the electric power mode is determined, for example, because of a decrease in an extent of opening of an accelerator.